It is known that in a composite of fiber reinforced matrix having the fiber oriented in substantially a single direction, the strength and modulus of the composite is greater in the direction of orientation. It is also known that extruding a composite comprising a matrix and fiber tends to orient the fiber in the direction of flow, i.e., the fibers become oriented parallel to the axis of the extrudate. However, it is often desirable to produce extruded products having the fibers oriented in other directions than parallel to the axis of the extrudate. For example, because the bursting forces in a hose under pressure are greater around the circumference than along the axis, it is necessary that a hose possess adequate physical properties in the hoop direction for which purpose substantial orientation of the fiber in the hoop direction is desirable.
Hose and similar hollow or partially hollow articles are commonly formed by forcing a stream of plastic material over a mandrel of a die so as to divide and divert the stream into a channel formed between the mandrel and an outer die member. To obtain off-axis orientation, Donald U.S. Pat. No. 3,279,501, proposed forcing fiber and plastic matrix through a channel having parallel sides formed between concentric cylinders while rotating the cylinders. The rotation provided opposing helical patterns of fiber orientation in respect to the inner and outer surfaces of the tube. Improvements were achieved by Cessna, U.S. Pat. No. 3,651,187, through use of a conical rotating die. He pointed out that since the circumferential velocity changed as the distance from the rotating surfaces increased in the system suggested by Donald, the fibers were pulled into cylindrical surfaces of constant circumferential velocity but that, except at the forming surfaces, there was little off-axis orientation. By use of a conical rotating die, the circumferential velocity was made to vary longitudinally as well as radially. After being formed into cylindrical surfaces of constant circumferential velocity as before, the fiber in a given surface, if not perpendicular to the longitudinal axis of the channel, was subjected to varying circumferential speeds along its length so that the faster moving liquid tended to drag the fiber into its plane thereby orienting the fiber into a single longitudinal and annular plane. A further improvement suggested was to taper the sides of a diverging channel so that the outlet and inlet areas were substantially constant. Extending the length of the opening in the front of the extruder and simultaneously increasing the cross-sectional area of the opening, according to Parsons et al. U.S. Pat. No. 2,332,829, tends to turn particles more or less perpendicular to the axis of extrusion in a radial direction.